Etching of a phosphosilicate glass film selectively implanted with boron

Abstract

The etch rate of phosphosilicate glass becomes lowered as boron ions are implanted therein. In accordance with the principle of the present invention, boron ions are implanted into a phosphosilicate glass film selectively in location or concentration and the thus boron-implanted phosphosilicate glass film is etched by an etchant, for example buffered hydrofluoric acid solution, to etch an intended portion of the phosphosilcate glass film preferentially thereby defining a hole, such as a contact hole, or substantially flat surface.

What is claimed is: 
     
       1. A process for forming a hole in a phosphosilicate glass film formed on an underlying structure, comprising the steps of: introducing ions of selected material into said phosphosilicate glass film so as to define a desired concentration profile of said ions in said film, said ions of selected material causing to lower an etch rate of said phosphosilicate glass film when introduced therein;   forming a mask having a desired pattern on said phosphosilicate glass film; and   etching said phosphosilicate glass film to define a hole therein using the pattern of said mask.   
     
     
       2. The process of claim 1 wherein said selected material includes boron. 
     
     
       3. The process of claim 2 wherein said concentration profile is such that the concentration of introduced boron ions generally increases as it goes deeper from the exposed surface of said phosphosilicate glass film. 
     
     
       4. The process of claim 3 wherein said step of introducing is carried out by ion implantation. 
     
     
       5. The process of claim 4 wherein said ion implantation step is carried out at the energy level of 200 KeV or more at the dose of 1×10 17  ions/cm 2  or more. 
     
     
       6. The process of claim 5 wherein said step of etching is carried out using 15:1 buffered hydrofluoric acid solution. 
     
     
       7. A process for forming a hole in a phosphosilicate glass film formed on an underlying structure, comprising the steps of: forming a resist pattern on the surface of said phosphosilicate glass film at a location where said hole is to be formed in said phosphosilicate glass film;   introducing ions of selected material into said phosphosilicate glass using said resist pattern as a mask, said ions of selected material causing to lower an etch rate of said phosphosilicate glass film when introduced therein;   removing said resist pattern; and   subjecting the entire exposed surface of said phosphosilicate glass film to a selected etchant thereby causing that portion of said phosphosilicate glass which was covered by said resist pattern during the step of introducing to have that portion etched away at a faster etch rate than the rest.   
     
     
       8. The process of claim 7 wherein said step of introducing includes an ion implantation step for implanting boron ions into said phosphosilicate glass film where not covered by said resist pattern. 
     
     
       9. The process of claim 8 wherein said ion implantation step is carried out at the energy level in the order of 50 KeV with the dose of 1×10 17  ions/cm 2  or more. 
     
     
       10. The process of claim 9 wherein said selected etchant is 15:1 buffered hydrofluoric acid solution. 
     
     
       11. A process for flattening an exposed surface of a phosphosilicate glass film formed on an underlying structure having a raised portion at its top surface, said phosphosilicate glass film defining a projection corresponding to said raised portion, comprising the steps of: forming a resist pattern as covering at least said projection of said phosphosilicate glass film;   introducing ions of selected material into said phosphosilicate glass film using said resist pattern as a mask, said ions of selected material causing to lower an etch rate of said phosphosilicate glass film when introduced therein;   removing said resist pattern; and   subjecting the entire exposed surface of said phosphosilicate glass film to a selected etchant thereby causing said projection of phosphosilicate glass film to be etched away partly at an etch rate higher than the rest to thereby define a substantially flat surface.   
     
     
       12. The process of claim 11 wherein said resist pattern extends laterally over a predetermined distance beyond the edge of said raised portion. 
     
     
       13. The process of claim 12 wherein said predetermined distance is approximately 1 micron. 
     
     
       14. The process of claim 12 wherein said step of introducing includes a step of ion implantation using boron as said selected material.